The invention relates to a stopper for a pressure container, in particular for a container containing a fluid under pressure, such as beer.
For the closing of pressure containers having a generally circular opening, a hole fitting has previously been used which has an inner through-bore closed at its lower end by means of a cover. The cover is a form-fit connection with the hole fitting and is thus prevented from being pushed out from the inside through the hole fitting by the pressure present in the interior of the container. Thus, after the filling of the container, the hole fitting closed in this manner at its lower end is pressed into the opening of the container lid. The edge of the lid then snaps into an annular groove on the outside of the hole fitting, so as to prevent the hole fitting from sliding axially. The inner bore is thereby closed only at its lower end and for protection against soiling a dust cap is pressed into the top end of the hole fitting to close it.
To open the stopper, the dirt or dust cap is first removed by hand. The shaft of a dispenser or discharge fitting is then inserted into the inner bore of the hole fitting, and lies tightly against the inner surface of the hole fitting when slid in. On being slid in still further, the shaft pushes into the interior of the container the cover of which closes the inner bore at its bottom end. The container interior is then sealed by the shaft lying tightly against the inner wall of the hole fitting. The liquid in the container, e.g. beer, can then be dispensed using the discharge fitting.
This stopper is constructionally expensive as it consists of three separate pieces. A further drawback is that in practice the dust cap must have an opening through which the sealed inner bore is connected to the atmosphere. If the cover is then not completely tight, with the result that liquid residues such as beer residues collect inside the inner bore, then these can quickly decay under the influence of the entering air. When the stopper is to be opened, these decayed liquid quantities can only be removed from the inner bore with difficulty, or indeed not at all, and they are usually forcibly pushed into the container with the hole fitting. Such a stopper does therefore not satisfy hygiene requirements for the use of such stoppers in drink containers.
In order to prevent such dirt collection in the inner bore, the inner bore has been closed at its lower end with a plug which nearly completely fills the inner bore when slid in. In a known construction, the cover which closes the inner bore at its lower end is extended in a substantially cylindrical form as far as the region of the upper edge of the inner bore. In order to obtain good sealing, this cylinder-shaped plug is constructed of a harder material than that of the hole fitting which surrounds it.
Although this stopper can dispense with a separate dust seal, soiling in the region of the inner bore of such an assembly is however not completely eliminated. As the inner core typically ends at a small distance from the top end of the hole fitting, a depression is formed in the central region of the hole fitting which comprises an edge at the boundary surface between the inner bore and the top of the plug. Dirt residues can deposit in the region of this edge, which is relatively inaccessible for difficult cleaning.
Because of the substantially cylindrical construction of the plug in its upper region, it becomes much more difficult to squeeze the hole fitting into the hole in the vicinity of the annular groove provided along its circumference. In order to press the hole fitting, closed by the plug, into the opening in the container lid, a substantially higher force must therefore be applied, which not only makes the stopper more difficult to insert in practice, but can also lead to damage of a thin container lid.